A convoy of 280 Russian trucks headed for Ukraine, which Moscow says is carrying relief goods for war-weary civilians, has suddenly changed course, according to a Ukrainian state news agency.

With thousands of Russian troops still posted near the Ukrainian border and Ukraine's military putting increasing pressure on pro-Russian fighters around the city of Donetsk, many in Ukraine and elsewhere fear that the so-called humanitarian mission is actually an attempt to smuggle supplies to pro-Russian rebels.

The International Committee of the Red Cross contacted the aid convoy in the Rostov region, the organization said Thursday via Twitter. The group said it would discuss with Ukrainian officials how the operation will be conducted.

Photos: Crisis in Ukraine 104 photos

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels fire artillery Tuesday, October 14, at Donetsk Sergey Prokofiev International Airport, which is on the outskirts of Donetsk, Ukraine. Fighting between Ukrainian troops and pro-Russian rebels in the country has left more than 3,000 people dead since mid-April, according to the United Nations.

Hide Caption

1 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke rises behind the train station in Donetsk, Ukraine, during an artillery battle between pro-Russian rebels and Ukrainian government forces on Sunday, October 12.

Hide Caption

2 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian President Petro Poroshenko, center, inspects Ukrainian army positions close to Donetsk on Friday, October 10.

Hide Caption

3 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – The main terminal of Donetsk Sergey Prokofiev International Airport is hit by shelling during fighting between pro-Russian rebels and Ukrainian forces on Wednesday, October 8.

Hide Caption

4 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels fire mortars toward Ukrainian positions near to the Donetsk airport on October 8.

Hide Caption

5 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel walks past a burning house after shelling in the town of Donetsk, Ukraine, on Sunday, October 5.

Hide Caption

6 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – An Ukrainian sniper aims his weapon at a checkpoint near Popasna, Ukraine, on Thursday, October 2.

Hide Caption

7 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke rises from the area near the Donetsk airport after heavy shelling on October 2.

Hide Caption

8 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – An injured man is transported at a hospital after shelling in Donetsk on Wednesday, October 1.

Hide Caption

9 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A woman injured at a bus station cries at a Donetsk hospital on October 1.

Hide Caption

10 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel guards a damaged school in Donetsk on October 1.

Hide Caption

11 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian servicemen patrol in the Donetsk region on Friday, September 26.

Hide Caption

12 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel guards a destroyed bridge in Nyzhnya Krynka, Ukraine, on Tuesday, September 23.

Hide Caption

13 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Residents clean up debris at a building damaged by rockets in Debaltseve, Ukraine, on Monday, September 22.

Hide Caption

14 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A firefighter checks out a damaged office building after shelling in Donetsk on Sunday, September 21.

Hide Caption

15 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian soldier guards pro-Russian rebels during a prisoner exchange near Donetsk on September 21.

Hide Caption

16 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Members of the Ukrainian military, held as prisoners of war, sit in a bus waiting to be exchanged near Donetsk on Saturday, September 20.

Hide Caption

17 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke rises after an explosion at a weapons factory controlled by pro-Russian rebels near Donetsk on September 20. The cause of the explosion was not immediately known.

Hide Caption

18 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian helicopter patrols an area near Donetsk on September 20.

Hide Caption

19 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A firefighter walks past the rubble of a building destroyed by shelling in Donetsk on Wednesday, September 17.

Hide Caption

20 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A protester holds a smoke bomb during a demonstration outside the Presidential Palace in Kiev, Ukraine, on September 17. Activists protested the adoption of legislation giving greater autonomy to rebel-held parts of eastern Ukraine's Donetsk and Luhansk regions.

Hide Caption

21 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A man covers the body of his mother, who was killed on a bus during a battle in Donetsk on Tuesday, September 16.

Hide Caption

22 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – People walk through a market Monday, September 15, in the Kievsky district of Donetsk.

Hide Caption

23 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke rises around the Donetsk International Airport on Saturday, September 13, as shelling continues between pro-Russian rebels and the Ukrainian army.

Hide Caption

24 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian soldier stands guard as residents rally in support of a united Ukraine in the southern Ukrainian city of Mariupol on September 13.

Hide Caption

25 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Russian trucks, flying Russian flags and carrying humanitarian aid for eastern Ukraine, line up at a border checkpoint in Donetsk on September 13.

Hide Caption

26 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Workers unload supplies from Russia in Luhansk, Ukraine, on September 13. More than 200 Russian trucks entered Ukraine with supplies for the city, which has been cut off from electricity and water for weeks.

Hide Caption

27 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian soldiers ride on an armored vehicle near Kramatorsk, Ukraine, on September 13.

Hide Caption

28 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – People look at a large crater from a reported missile strike that hit a bus station Friday, September 12, in Makiivka, Ukraine.

Hide Caption

29 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Workers clear rubble Thursday, September 11, after the bombing of a mine in Donetsk.

Hide Caption

30 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A column of Ukrainian forces is seen in Volnovakha, Ukraine, on September 11.

Hide Caption

31 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – An elderly woman sits next to a Ukrainian soldier standing guard in Volnovakha on September 11.

Hide Caption

32 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Armed pro-Russian rebels walk September 11 in front of the destroyed Luhansk International Airport. The rebels took control of the airport on September 1 after heavy fighting with the Ukrainian army.

Hide Caption

33 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Residents of Lutuhyne, Ukraine, push containers in a wheelbarrow September 11 as they walk between destroyed armored vehicles left behind by the Ukrainian army.

Hide Caption

34 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian troops protect themselves from a nearby shooting in Debaltseve on Tuesday, September 9.

Hide Caption

35 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Young residents of Berdyansk, Ukraine, dig trenches September 9 to help Ukrainian forces protect the city from possible rebel attacks.

Hide Caption

36 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian President Petro Poroshenko, left, inspects military personnel during a visit to Mariupol on Monday, September 8.

Hide Caption

37 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel stands next to a truck with a heavy machine gun attached to it Sunday, September 7, in Donetsk.

Hide Caption

38 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Homes smolder after being hit by shelling in Donetsk on September 7.

Hide Caption

39 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A woman stands next to a road sign September 7 after an overnight bombing attack at an Ukrainian army checkpoint on the outskirts of Mariupol.

Hide Caption

40 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian troops stand on a deserted road as they patrol the border area of the Donetsk and Luhansk regions Friday, September 5, near Debaltseve.

Hide Caption

41 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A man repairs damage to a building caused by shelling in Donetsk on September 5.

Hide Caption

42 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke rises on the outskirts of Mariupol after pro-Russian rebels fired heavy artillery on September 5.

Hide Caption

43 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian soldiers ride a tank on a road close to where pro-Russian rebels fired heavy artillery outside Mariupol on September 5.

Hide Caption

44 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A wounded Ukrainian soldier is helped by a medical team on the outskirts of Mariupol on September 5.

Hide Caption

45 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel holds a destroyed weapon in the village of Novokaterynivka, Ukraine, on Thursday, September 4.

Hide Caption

46 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Unmarked military vehicles burn on a country road in Berezove, Ukraine, on September 4 after a clash between Ukrainian troops and pro-Russian rebels. For months, Ukrainian government forces have been fighting the rebels near Ukraine's eastern border with Russia.

Hide Caption

47 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – People wait by their cars near Berezove on September 4 as rockets hit the road ahead.

Hide Caption

48 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel holds a dog, which has a hand grenade attached to its leash, in Donetsk on Wednesday, September 3.

Hide Caption

49 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels fire at Ukrainian army positions in Donetsk on September 3.

Hide Caption

50 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian military vehicle patrols in the Donetsk region on September 3.

Hide Caption

51 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels hold a man near a column of destroyed Ukrainian military vehicles in Novokaterynivka on Tuesday, September 2.

Hide Caption

52 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian military truck passes by a serviceman resting in his military camp in Ukraine's Donetsk region on September 2.

Hide Caption

53 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A destroyed Ukrainian military vehicle sits abandoned on the side of the road near Novokaterynivka on September 2.

Hide Caption

54 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Men clear rubble in Ilovaisk, Ukraine, on Sunday, August 31.

Hide Caption

55 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian troops leave the rebel-held town of Starobesheve on Saturday, August 30.

Hide Caption

56 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian loyalist fighter from the Azov Battalion stands guard on a hill on the outskirts of Mariupol on August 30.

Hide Caption

57 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel listens to the news on a transistor radio in the town of Novoazovsk, Ukraine, on Friday, August 29.

Hide Caption

58 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian soldiers stop on a roadside as they wait for the start of their march into Mariupol on Wednesday, August 27.

Hide Caption

59 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A man opens a box filled with rocket-propelled grenades left by the Ukrainian army in Starobesheve.

Hide Caption

60 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel walks through a local market damaged by shelling in Donetsk on Tuesday, August 26.

Hide Caption

61 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian servicemen of the volunteer battalion Azov leave for Novoazovsk on August 26.

Hide Caption

62 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels escort captured Ukrainian soldiers in a central square in Donetsk on Sunday, August 24.

Hide Caption

63 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – People yell as Ukrainian prisoners are paraded through Donetsk in eastern Ukraine on August 24.

Hide Caption

64 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel delivers a speech atop a damaged Ukrainian armored personnel carrier in Donetsk on August 24.

Hide Caption

65 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – People look at damaged Ukrainian military equipment in Donetsk on August 24.

Hide Caption

66 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – The first trucks of a Russian aid convoy roll on the main road to Luhansk in eastern Ukraine on Friday, August 22. The head of Ukraine's security service called the convoy a "direct invasion" under the guise of humanitarian aid since it entered the country without Red Cross monitors.

Hide Caption

67 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel holds shrapnel from a rocket after shelling in Donetsk on August 22.

Hide Caption

68 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Residents sit in a makeshift bomb shelter during a shelling in Makiivka on Wednesday, August 20.

Hide Caption

69 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Dogs play together as a Russian convoy carrying aid supplies stops at a border control point with Ukraine on August 20.

Hide Caption

70 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian forces take their position not far from Luhansk on August 20.

Hide Caption

71 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Clouds of smoke are on the horizon as Ukrainian forces and pro-Russian rebels clash in Yasynuvata, Ukraine, on Tuesday, August 19.

Hide Caption

72 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – An Ukrainian helicopter flies near Kramatorsk on August 19.

Hide Caption

73 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian soldiers load a missile during fighting with pro-Russian rebels Monday, August 18, near Luhansk.

Hide Caption

74 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Boys play at a refugee camp, set up by the Russian Emergencies Ministry, near the Russian-Ukrainian border on August 18.

Hide Caption

75 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian soldiers carry weapons at a checkpoint near Debaltseve on Saturday, August 16.

Hide Caption

76 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels greet each other as they pass near Krasnodon, Ukraine, on August 16.

Hide Caption

77 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A fireman tries to extinguish a fire after shelling in Donetsk on August 16.

Crisis in Ukraine – Trucks of a Russian humanitarian convoy are parked in a field outside the town of Kamensk-Shakhtinsky, in the Rostov region of Russia about 20 miles from the Ukraine border, on August 15. Ukrainian officials were preparing to inspect the convoy, which was bound for the conflict-torn east.

Hide Caption

80 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A truck driver from the convoy jumps out of a trailer on August 15. The Ukrainian government had expressed fears that the convoy was a large-scale effort to smuggle supplies or troops to pro-Russian rebels.

Hide Caption

81 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A tank belonging to pro-Russian rebels moves along a street in Donetsk on August 15.

Hide Caption

82 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian soldier walks past a line of self-propelled guns as a column of military vehicles prepares to head to the front line near Ilovaisk on Thursday, August 14.

Hide Caption

83 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A Ukrainian soldier prepares a mortar at a position near Ilovaisk on August 14.

Hide Caption

84 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A man inspects damage at his house after a shelling in Donetsk on August 14.

Hide Caption

85 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A convoy of trucks, which Moscow said was carrying relief goods for war-weary civilians, moves from Voronezh, Russia, toward Rostov-on-Don, Russia, on August 14.

Hide Caption

86 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Pro-Russian rebels on the outskirts of Donetsk stand at a checkpoint near a bullet-riddled bus on Wednesday, August 13.

Hide Caption

87 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel inspects damage after shelling in Donetsk on Thursday, August 7.

Hide Caption

88 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Smoke billows from a Ukrainian fighter jet crash near the village of Zhdanivka, Ukraine, on August 7.

Hide Caption

89 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Residents of eastern Ukraine cry in a hospital basement being used as a bomb shelter August 7 in Donetsk.

Hide Caption

90 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ordnance from a Ukrainian rocket launcher shoots toward a pro-Russian militant position in the Donetsk region on August 7.

Hide Caption

91 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Relatives of Ukrainian military member Kyril Andrienko, who died in combat in eastern Ukraine, gather during his funeral in Lviv, Ukraine, on August 7.

Hide Caption

92 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Refugees from southeastern Ukraine wait at a refugee camp in Donetsk on Wednesday, August 6.

Hide Caption

93 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian rebel adjusts his weapon in Donetsk on August 6.

Hide Caption

94 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Men walk past a bomb crater in Donetsk on August 6.

Hide Caption

95 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A man steps out of his car as Ukrainian soldiers inspect the vehicle at a checkpoint in Debaltseve on August 6.

Hide Caption

96 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian servicemen sit on a bus near Slovyansk, Ukraine, on Tuesday, August 5.

Hide Caption

97 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A pro-Russian separatist guards a road as Australian, Malaysian and Dutch investigators prepare to examine the crash site of Malaysia Airlines Flight 17 near the village of Rossipne, Ukraine, on August 5. U.S. and Ukrainian officials allege that a Russian-made missile shot down the plane from rebel-held territory, killing all 298 people on board. Russia and the rebel fighters deny involvement.

Hide Caption

98 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Rescue workers carry the body of a woman who was killed during a bomb shelling in Donetsk on August 5.

Hide Caption

99 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – A boy stands in a hallway of a refugee hostel run by pro-Russian rebels in Donetsk on Monday, August 4.

Hide Caption

100 of 104

Photos: Crisis in Ukraine104 photos

Crisis in Ukraine – Ukrainian servicemen from the Donbass volunteer battalion clean their guns Sunday, August 3, in Popasna, Ukraine.

MUST WATCH

JUST WATCHED

Ukrainian military tries to retake Donetsk

MUST WATCH

The convoy was seen earlier in the day 25 miles from the Ukrainian border in the Rostov region, according to video shot and distributed by Reuters.

If the trucks cross the border and before they reach the area controlled by separatists, they would have to be examined by Ukrainian border guards, a Ukrainian security official said.

At that point, the convoy would be handed over to Red Cross representatives, the official said.

The office of the Ukrainian counterterrorism operation said Thursday it could not confirm that the convoy has crossed on the Ukrainian side. The Ukrainian border service denied reports that the convoy had crossed from Russia.

"All responsibility for the safety of this convoy lays with Russia because it is controlling armed mercenaries there," Ukrainian national security and defense council spokesman Andeiy Lysenko told reporters in Kiev.

The truckshad been expected to arrive at a checkpoint in Kharkiv on Wednesday but bypassed that route, according to the website Ukrinform. It's not clear what route the convoy will now take.

"In Donbas," Lubkivsky said, referring to the war-torn eastern region of Ukraine that includes the contested cities of Donetsk and Luhansk, "they are trying to use the pretext of humanitarian aid and assistance."

Without offering proof, Ukrainian officials have even accused Russia of repainting military vehicles white to disguise their efforts.

In Kiev, where many loyalties lie with the Ukrainian government, skepticism of Russian President Vladimir Putin's motive was rampant among residents.

"Normal people do not send guns to kill people and food for them to eat in the same cars," said IT specialist Igor Vlasenko. "I think most Ukrainians want him to leave Ukraine alone. We can help ourselves."

And it's not just the Ukrainians raising concerns about a possible Russian Trojan horse.

Red Cross flummoxed

In an interview Monday with Reuters, NATO Secretary General Anders Fogh Rasmussen spoke of a "high probability" that Russia will invade Ukraine.

"We see the Russians developing the narrative and the pretext for such an operation under the guise of a humanitarian operation, and we see a military buildup that could be used to conduct such illegal military operations in Ukraine," he said.

Russia has acknowledged sending the convoy. In a conversation Monday with the President of the European Commission, Putin said his country was working with the International Committee of the Red Cross to deliver aid to civilians suffering as a result of savage fighting there.

Except the Red Cross said at the time that it didn't know what Putin was talking about.

Spokesman Andrew Loersch said the agency doesn't have any agreement with Russia on such a convoy.

And Red Cross European operations chief Laurent Corbaz said Tuesday in Geneva that the agency hasn't gotten much clarity from Moscow about its purported role in the operation, including how the aid would be handed over and security guarantees for Red Cross workers.

"We said that we could be on board but that we needed to have some clarification first regarding modalities, practical steps that have to be implemented prior to a launch of such an operation," he said.

According to the Russian news agency Itar-Tass, the shipment is bound for Luhansk and contains 400 tons of grain, 100 tons of sugar, 62 tons of baby food, 54 tons of medical supplies, sleeping bags and "electrical power units."

At the opening of a Ukraine Cabinet meeting on Wednesday, Prime Minister Arseniy Yatsenyuk said that "Ukraine can receive humanitarian aid exclusively through the Red Cross and within international legal framework."

'False pretense'

But after an incident Saturday in which Ukrainian officials claim to have stopped a purported aid convoy accompanied by Russian troops, Ukraine has vowed to stop any "uncertified" aid convoy from Russia.

In the Saturday incident, Ukraine's Deputy Head of the Presidential Administration Valeriy Chaly told a Ukrainian television channel that the convoy was nothing more than a Russian provocation.

JUST WATCHED

Will NATO protect Ukraine from Russia?

MUST WATCH

JUST WATCHED

Explore a Ukrainian ghost town

MUST WATCH

Explore a Ukrainian ghost town02:02

PLAY VIDEO

"Under a false pretense of agreement with the International Committee of the Red Cross in Ukraine, a humanitarian convoy of 'peacekeepers' was ready to enter the country, apparently in order to provoke a full-scale conflict," he said.

U.S. officials have warned Russia against using aid as a means of wading deeper into the Ukraine conflict.

At a U.N. Security Council meeting Saturday, U.S. Ambassador Samantha Power said Russia has no business delivering aid in Ukraine when international aid groups are better equipped to do the job.

"Therefore, any further unilateral intervention by Russia into Ukrainian territory -- including one under the guise of providing humanitarian aid -- would be completely unacceptable and deeply alarming," she said. "And it would be viewed as an invasion of Ukraine."

Secretary of State John Kerry made a similar point with his Russian counterpart on Saturday, according to the State Department.

While Western leaders have refused any suggestion that Russian acts could draw NATO nations into war over Ukraine, they do say it would lead to even stricter economic sanctions against Russia than those already imposed by the United States and the European Union.

So far, Russian officials have shrugged off the sanctions.

Rebels on the ropes?

Moscow's decision to send the convoy comes as about 50,000 Ukrainian troops press forward with an offensive to rout rebel fighters from Donetsk.

They have put increasing pressure on the rebel fighters, and Ukrainian officials say they expect to be able to fully recapture the city by Ukraine's Independence Day on August 24.

The ongoing fighting -- sparked last year with a political crisis over whether Ukraine would seek closer ties with Europe or Russia -- has left more than 2,000 people dead and just under 5,000 wounded in eastern Ukraine since mid-April, according to estimates from U.N. officials that they called "conservative." The officials say the death toll has been on the rise in recent days, with reports of at least 41 killed and 143 wounded on Thursday alone.

Hundreds of thousands have been forced to flee their homes and seek shelter either elsewhere in Ukraine or across the border in Russia, the United Nations says.